132 research outputs found
Population pulsation resonances of excitons in monolayer MoSe2 with sub 1 {\mu}eV linewidth
Monolayer transition metal dichalcogenides, a new class of atomically thin
semiconductors, possess optically coupled 2D valley excitons. The nature of
exciton relaxation in these systems is currently poorly understood. Here, we
investigate exciton relaxation in monolayer MoSe2 using polarization-resolved
coherent nonlinear optical spectroscopy with high spectral resolution. We
report strikingly narrow population pulsation resonances with two different
characteristic linewidths of 1 {\mu}eV and <0.2 {\mu}eV at low-temperature.
These linewidths are more than three orders of magnitude narrower than the
photoluminescence and absorption linewidth, and indicate that a component of
the exciton relaxation dynamics occurs on timescales longer than 1 ns. The
ultra-narrow resonance (<0.2 {\mu}eV) emerges with increasing excitation
intensity, and implies the existence of a long-lived state whose lifetime
exceeds 6 ns.Comment: (PRL, in press
Anisotropy of thermal conductivity oscillations in relation to the Kitaev spin liquid phase
In the presence of external magnetic field, the Kitaev model could either
hosts gapped topological anyon or gapless Majorana fermions. In
-RuCl, the gapped and gapless cases are only separated by a
thirty-degree rotation of the in-plane magnetic field vector. The
presence/absence of the spectral gap is key for understanding the thermal
transport behavior in -RuCl. Here, we study the anisotropy of the
oscillatory features of thermal conductivity in -RuCl. We examine
the oscillatory features of thermal conductivities (k//a, k//b) with fixed
external fields and found distinct behavior for the gapped (B//a) and gapless
(B//b) scenarios. Furthermore, we track the evolution of thermal resistivity
() and its oscillatory features with the rotation of in-plane
magnetic fields from B//b to B//a. The thermal resistivity
display distinct rotational symmetries before and after the emergence of the
field induced Kitaev spin liquid phase. These experiment data suggest close
correlations between the oscillatory features of thermal conductivity, the
underlying Kitaev spin liquid phase and the fermionic excitation it holds
Stacking disorder in -RuCl via x-ray three-dimensional difference pair distribution function analysis
The van der Waals layered magnet -RuCl offers tantalizing
prospects for the realization of Majorana quasiparticles. Efforts to understand
this are, however, hampered by inconsistent magnetic and thermal transport
properties likely coming from the formation of structural disorder during
crystal growth, postgrowth processing, or upon cooling through the first order
structural transition. Here, we investigate structural disorder in
-RuCl using x-ray diffuse scattering and three-dimensional
difference pair distribution function (3D-PDF) analysis. We develop a
quantitative model that describes disorder in -RuCl in terms of
rotational twinning and intermixing of the high and low-temperature structural
layer stacking. This disorder may be important to consider when investigating
the detailed magnetic and electronic properties of this widely studied
material.Comment: 6 pages; 3 figures; accepted in Physical Review
Nanometer-Scale Lateral p–n Junctions in Graphene/α-RuCl3 Heterostructures
[EN] The ability to create nanometer-scale lateral p-n junctions is essential for the next generation of two-dimensional (2D) devices. Using the charge-transfer heterostructure graphene/alpha-RuCl3, we realize nanoscale lateral p-n junctions in the vicinity of graphene nanobubbles. Our multipronged experimental approach incorporates scanning tunneling microscopy (STM) and spectroscopy (STS) and scattering-type scanning near-field optical microscopy (s-SNOM) to simultaneously probe the electronic and optical responses of nanobubble p-n junctions. Our STM/STS results reveal that p-n junctions with a band offset of 0.6 eV can be achieved with widths of 3 nm, giving rise to electric fields of order 108 V/m. Concurrent s-SNOM measurements validate a point-scatterer formalism for modeling the interaction of surface plasmon polaritons (SPPs) with nanobubbles. Ab initio density functional theory (DFT) calculations corroborate our experimental data and reveal the dependence of charge transfer on layer separation. Our study provides experimental and conceptual foundations for generating p-n nanojunctions in 2D materials.Research at Columbia University was supported as part of the Energy Frontier Research Center on Programmable Quantum Materials funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under Award No DE-SC0019443. Plasmonic nano-imaging at Columbia University was supported by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under Award No DE-SC0018426. J.Z. and A.R. were supported by the European Research Council (ERC-2015-AdG694097), the Cluster of Excellence “Advanced Imaging of Matter” (AIM) EXC 2056-390715994, funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under RTG 2247, Grupos Consolidados (IT1249-19), and SFB925 “Light induced dynamics and control of correlated quantum systems”. J.Z. and A.R. would like to acknowledge Nicolas Tancogne-Dejean and Lede Xian for fruitful discussions and also acknowledge support by the Max Planck Institute-New York City Center for Non-Equilibrium Quantum Phenomena. The Flatiron Institute is a division of the Simons Foundation. J.Z. acknowledges funding received from the European Union Horizon 2020 research and innovation programme under Marie Skłodowska-Curie Grant Agreement 886291 (PeSD-NeSL). STM support was provided by the National Science Foundation via Grant DMR-2004691. C.R.-V. acknowledges funding from the European Union Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement 844271. D.G.M. acknowledges support from the Gordon and Betty Moore Foundation’s EPiQS Initiative, Grant GBMF9069. J.Q.Y. was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. S.E.N. acknowledges support from the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Division of Scientific User Facilities. Work at University of Tennessee was supported by NSF Grant 180896
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Neutron scattering in the proximate quantum spin liquid α-RuCl3.
The Kitaev quantum spin liquid (KQSL) is an exotic emergent state of matter exhibiting Majorana fermion and gauge flux excitations. The magnetic insulator α-RuCl3 is thought to realize a proximate KQSL. We used neutron scattering on single crystals of α-RuCl3 to reconstruct dynamical correlations in energy-momentum space. We discovered highly unusual signals, including a column of scattering over a large energy interval around the Brillouin zone center, which is very stable with temperature. This finding is consistent with scattering from the Majorana excitations of a KQSL. Other, more delicate experimental features can be transparently associated with perturbations to an ideal model. Our results encourage further study of this prototypical material and may open a window into investigating emergent magnetic Majorana fermions in correlated materials
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